A molded case circuit breaker containing a common trip unit and accessory module for field installation of optional accessory function is described within U.S. patent application Ser. No. 882,989, filed July 7, 1986, and entitled "Combined Trip Unit And Accessory Module For Electronic Trip Circuit Breaker". The circuit breaker uniquely contains the current sensing transformers and signal processing electronics within a common enclosure with the circuit breaker operating mechanism. The combined trip unit and accessory module provide overcurrent, shunt trip and undervoltage release facility to the breaker by means of a common trip actuator assembly. The Application is incorporated herein for reference purposes and should be reviewed for its teaching of the mechanical interaction of the trip unit and accessory module with the circuit breaker interruption mechanism.
U.S. patent application Ser. No. 817,213, filed Jan. 8, 1986, and entitled "Interchangeable Mechanism For Molded Case Circuit Breaker", describes a compact circuit breaker operating mechanism, which is automatically assembled, in part, and which is interchangable within breakers of different ampere ratings. This Application is incorporated for reference purposes and should be reviewed for its description of an operating mechanism similar to that used within the circuit breaker of the instant invention.
Molded case circuit breakers provide overcurrent protection by responding to current levels within a protected circuit in excess of predetermined current thresholds. In both residential as well as in lower rating industrial breakers, a thermal-magnetic trip unit responds to such threshold currents by contacting and articulating the operating mechanism to separate the breaker contacts. Electronic trip units are feasibly employed within those industrial circuit breakers of higher ampere ratings and require an intermediate actuator to articulate the operating mechanism, usually in the form of a magnetically-latched solenoid. A current pulse to the solenoid generates an opposing magnetic flux allowing the actuator to release under the bias provided by a charged spring. When a common overcurrent and accessory trip unit, such as described within the former referenced patent application is employed within such an industrial rated breaker, additional circuit logic must be provided for each accessory function. The overcurrent protection logic is provided by the electronic trip unit signal processor, which responds solely to overcurrent conditions. Separate logic circuits are required for undervoltage release units and shunt trip units.
One purpose of the instant invention is to provide an electronic control circuit for an undervoltage release unit coupled with a common actuator that separately provides overcurrent trip facility. The electronic circuit components for the undervoltage release unit are carried by a separate printed wiring board that is integral with the undervoltage release coil.